This invention relates to improved pyrolysis gas chromatograph specimen capsules and a process for analysis using said specimen capsules.
Generally in gas chromatography, a sample to be analyzed is placed in a vaporizer and vaporized by heating or by pyrolysis; the vaporized components are swept by a carrier gas into a column filled with a column packing; the components of the sample vapour are carried through the column at different rates, which are governed by their partition coefficient between the gas phase and the stationary phase. They emerge from the end of the column at different times. Their presence in the emerging carrier gas is detected by chemical or physical means.
It is desirable that the flow of carrier gas through the column packing should be continued while the column is not in service, namely during the preparation period, so as to keep the column packing under fixed conditions and protect it against possible degradation. The carrier gas flows in different paths during the analysis period and during the preparation period. The switch of the path of flow is effected by means of a valve which is placed in the piping of the carrier gas. In most gas chromatographs, the column and the vaporizer are encased in a constant temperature oven so as to be kept at a predetermined temperature.
In the conventional pyrolysis gas chromatograph, the switching valve is placed between the vaporizer and the column and, during the analysis period, the vaporized components of the sample are carried by the carrier gas from the vaporizer to the analyzing column via the valve. It is, therefore, necessary that the valve be placed inside the constant temperature oven and maintained at the constant temperature, so that the sample is prevented from being condensed while passing through the valve.
The switching valve is required to incorporate compressible packings of a rubbery material which serve the purpose of sealing. To satisfy the purpose, these parts are made of heat-proof plastics such as, for example, Teflon. Even Teflon that has properties most suited to the purpose cannot withstand temperatures higher than 170.degree. C. Thus, the temperature at which the constant temperature oven maintains the analyzing column is limited to the highest temperature that the aforementioned parts can withstand.
As concerns the injection of a sample into the vaporizer of the gas chromatograph, one known method accomplishes the injection by taking the sample in a micro-syringe, piercing the needle of this syringe through a rubber septum placed to close the entrance to the vaporizer and injecting the sample into the vaporizer.
When this method is applied to analyzing a volatile substance mingled with an involatile substance such as, for example, a solvent in a paint, the vaporization of the volatile component occurs first and requires a considerable length of time. Consequently, the sample tends to disperse prior to arrival at the column or it is found to be quite difficult to inject the entire sample to the column. There is another disadvantage that the residue of the sample cannot be extracted after completion of the analysis and it is left to contaminate the vaporizer and the column.
In other methods, the sample is injected into the vaporizer and thermally decomposed therein by the action of heat. There is known, for example, a method comprising the steps of having a sample solution deposited on the surface of a ferromagnetic metal wire about 0.6 mm in diameter and about 20 mm in length, drying the solution, inserting the wire into the vaporizer, exposing the wire to an alternate current magnetic field thereby inducing it to radiate heat and pyrolyzing the sample deposited on the wire. Since this method requires the sample to be deposited on the surface of the wire, the applicability of this method is limited to liquid samples or to solid samples which can be dissolved with solvents into solutions. The method is not applicable to solid insoluble samples. When a given solid sample is converted into a liquid sample by the use of a suitable solvent, the liquid sample is deposited on the wire and subsequently dried free of the solvent. From the practical point of view, however, thorough removal of the solvent content from the deposited sample is an impossibility. The gas produced from the deposited sample by pyrolysis, therefore, entrains the solvent component. This means that the chromatogram obtained by this method does not represent accurate analysis of the solid sample in the form thoroughly free from foreign matter.
The amount of the sample solution which is deposited on the wire must also be considered. Even if the solution to be deposited is the same, it is impossible to have exactly the same amount of solution deposited on all the wires in use. In the case of an excess of deposit, the recording of the results of analysis becomes impracticable because the peaks protrude over the edge of the chart paper. One same solution is deposited on a plurality of wires and the results of analysis conducted on each wire are recorded. Therefore, there is involved the troublesome work of making proper adjustment on each wire so that the peaks do not protrude over the edge of the chart paper. The amount of sample thus deposited on the wire is quite small. In the case of an operation in which mass spectrum is simultaneously performed using a mass spectrometer connected next to the gas chromatograph, therefore, the amount of the sample on the wire is not sufficient, making it impossible to carry out the mass spectrometric identification.
It is an object of this invention to provide a specimen capsule for use in a gas chromatograph, which permits accurate analysis of the volatile substances contained in high boiling substances and further to provide a process for analysis using the specimen capsule.
It is another object of the present invention to provide a specimen capsule for pyrolysis which eliminates the necessity of a solvent even where the sample to be analyzed happens to be a solid substance and which is also usable where the sample is a liquid substance and further to provide a process for the analysis using said specimen capsule.
Yet another object of this invention resides in providing a specimen containing a constant amount of sample.